University of Texas at Austin

Monday, January 24, 2011

The view from an airborne observatory

NASA's SOFIA observatory flies over the desert north of Edwards Air Force Base, Calif., on a test flight.

NASA's SOFIA observatory flies over the desert north of Edwards Air Force Base, Calif., on a test flight.

University of Texas at Austin Astronomer Paul Harvey had a seat on one of the first flights of NASA’s new airborne observatory, SOFIA.

That acronym stands for Stratospheric Observatory for Infrared Astronomy.

The observatory is a Boeing 747-SP aircraft equipped with a 100-inch diameter telescope. It flies at 40,000 feet or so to get above absorption from the water vapor in the atmosphere.

“You get the advantage of still using an Earth-based telescope, but in the stratosphere above almost all the water vapor,” Harvey said. “So you can observe a large fraction of the infrared spectrum without too much of a problem.”

Harvey, a senior research scientist in the astronomy department who uses infrared telescopes to study how stars are born, also flew on SOFIA’s predecessor, the Kuiper Airborne Observatory, a C141 transport plane.

“When I got to the end of the (SOFIA) flight, I felt like I was on a Kuiper Airborne Observatory flight in terms of just the way the whole operation worked,” Harvey said. “It was comforting, in a way.”

The Kuiper mission flew for 21 years. SOFIA is just getting off the ground.

“There’s a moderate amount of confusion,” Harvey said of the flight, with a laugh. “Because everything’s being done in real time.”

Paul Harvey is a senior research scientist in the Department of Astronomy at The University of Texas at Austin.

Paul Harvey is a senior research scientist in the Department of Astronomy at The University of Texas at Austin.

With a space observatory like the Spitzer Space Telescope, which Harvey has used, the observation is programmed ahead of time.

“But here they’re trying to make sure the telescope is pointed in the right place,” he said. “Because it’s a new facility, things aren’t working as well as everyone hopes they will eventually. So there’ll be times when the computer crashes and we have to start up again.”

The observing instruments are in the rear of the aircraft and they point out the left side.

The front of the plane is set up like an open-office design. There are consoles with computers, where researchers quickly download the data streaming into the telescope, and tables where people can work. There’s an area toward the front where people can take a break.

Harvey had submitted a proposal for one of the first flights, but was told he probably wouldn’t be able to go. Then, the day before the flight, he got permission to board.

He had to rush to round up a certificate of good health from a doctor, a liability release from his employer and other items.

“It was a little bit of pandemonium,” Harvey said.

It turned out that the data for Harvey’s proposal had been collected on the previous SOFIA flight, but he welcomed the opportunity to fly because he’ll be on board for another project in the spring.

Cornell University scientists Luke Keller, seated, and Justin Schoenwald study data from the Faint Object InfraRed Camera for the SOFIA Telescope (FORCAST) mounted on the SOFIA telescope during a pre-flight rehearsal practice for the observatory’s initial science flight on Nov. 30, 2010.

Cornell University scientists Luke Keller, seated, and Justin Schoenwald study data from the Faint Object InfraRed Camera for the SOFIA Telescope (FORCAST) mounted on the SOFIA telescope during a pre-flight rehearsal practice for the observatory’s initial science flight on Nov. 30, 2010.

For this project, he used the combination of high image infrared resolution available with SOFIA and the Faint Object InfraRed CAmera for the SOFIA Telescope (FORCAST) to study the distribution of dust and gas around Sharpless 140, a young, forming star cluster. It’s about 3,000 light-years from Earth in the constellation Cepheus.

The FORCAST team from Cornell University captured images of the cluster, moving the telescope slightly between each image in order to sample every pixel multiple times.

“It’s a cluster of new stars, young stars that are fairly bright, fairly luminous and they’re close enough together that, with the Kuiper Observatory, they looked like one fuzzy object,” Harvey said. “With SOFIA, we can now tell there are three or four stars there at least.”

Dan Lester, another Texas astronomer, is also involved with SOFIA. An infrared instrument built by John Lacy, a Texas astronomy professor, will fly on SOFIA in a couple of years. He’s turned the telescope over to a former doctoral student, Matt Richter, who’s at the University of California, Davis, for the flights.

Harvey’s spring project will be to see whether a technique for obtaining high-resolution images, that’s been established in other contexts, will work with the FORCAST instrument.

It involves watching a star as the dark side of the moon crosses in front of it.

“You can actually resolve the size of the disk of the star with this technique because you can measure how long it takes for the light to go from full brightness to zero brightness,” Harvey said. “If you know how fast the moon’s moving in front of the star, that tells you how big the star is.”

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